API 653 Cheat Sheet 2026

The 30 highest-yield API 653 facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What is the role of non-destructive testing (NDT) in Fitness-for-Service evaluations? → NDT helps detect defects or weaknesses in the material, essential for FFS decisions.
2. Per API 653, what NDE method is required for detecting surface cracks in a weld on a non-magnetic (austenitic stainless steel) tank shell? → Liquid penetrant testing (PT)
3. According to API 653, what is the minimum hold time for a hydrostatic test on a reconstructed tank before inspection begins? → 1 hour
4. Which welding process is generally NOT acceptable per API 653 for structural repairs to tank shells without additional qualification? → Stud welding for structural attachments
5. What is the MOST important reason for API 653 Aboveground Storage Tank Inspector Certification professionals to maintain continuing education? → To stay current with evolving standards, practices, and regulations
6. What is the significance of the 'critical zone' at the tank bottom as defined in API 653? → The annular plate ring within 3 inches of the shell-to-bottom weld
7. Under API 653, who is responsible for determining the inspection interval for an aboveground storage tank? → A qualified API 653 inspector or engineer
8. What is the purpose of post-weld heat treatment (PWHT) when applied to a repaired tank shell section? → To relieve residual stresses and temper the heat-affected zone
9. In API 653, what must be done when a repaired or altered tank is returned to service with a reduced maximum allowable working level (MAWL)? → The reduction must be documented and the tank must be marked with the new MAWL
10. Which corrosion mechanism is characterized by localized attack beneath deposits, gaskets, or at crevices where oxygen is depleted? → Crevice corrosion
11. API 653 requires that inspection records be retained for at least how long after the tank is permanently removed from service? → 5 years
12. Which of the following is a type of cathodic protection system used on aboveground storage tank bottoms? → Sacrificial anode (galvanic) system
13. When applying the API 653 formula to calculate minimum acceptable shell thickness, which factor is NOT included in the standard calculation? → Wind load on the shell
14. Which factor is MOST critical when establishing the external inspection interval for a tank in a coastal marine environment? → Accelerated external corrosion due to salt air exposure
15. Which damage mechanism causes tank shell cracking when tensile stress combines with a corrosive environment, commonly seen in tanks storing caustic solutions? → Stress corrosion cracking
16. Which API 653 repair method is typically used to restore shell plate that has been corroded below the minimum required thickness? → Installing a flush patch using full-penetration butt welds
17. Which type of corrosion is characterized by localized attack that produces small pits or holes in the metal surface of a storage tank? → Pitting corrosion
18. What is the value of continuing education in documentation for API 653 professionals? → It keeps professionals current with evolving standards and practices
19. What does validity mean when selecting an assessment tool for API 653 certification purposes? → The tool measures what it claims to measure
20. API 653 states that settlement readings during a hydrostatic test should be taken at a minimum of how many equally spaced points around the tank circumference? → 8 points
21. Why are corrosion-related issues a primary focus in API 653 tank inspections? → Corrosion can lead to leaks and structural failure, which API 653 seeks to prevent.
22. What does API 653 define as a 'reconstruction' of a tank? → Relocation of a tank to a new site with reassembly
23. How is the welding process selected for a specific material? → Based on material type, thickness, and joint design.
24. A tank shell plate has a measured thickness of 0.285 inches. The tmin calculated per API 653 is 0.250 inches. What is the corrosion allowance remaining? → 0.035 inches
25. Which electrode classification would be selected when making low-hydrogen welds on A516 Grade 70 carbon steel in accordance with AWS A5.1? → E7018
26. Which type of assessment provides a snapshot of current status at a single point in time? → Baseline assessment
27. What action must be taken if a leak is discovered in the shell during a hydrostatic test under API 653? → Immediately reduce water level and repair before retesting
28. What does API 653 require regarding documentation of tank inspection and repair records? → Records must be kept for the life of the tank
29. A tank inspector identifies pitting on the internal shell surface. Which measurement is most critical for determining whether the shell remains fit for service? → The remaining wall thickness at the deepest pit location
30. What is the role of welding in the repair of damaged components during Fitness-for-Service evaluations? → Welding restores structural integrity to damaged components during repairs.